1. Field of the Invention
This invention relates to an ink jet recording head.
2. Description of the Prior Art
An ink jet recording method (liquid jet recording method) enables high speed recording because the noise generated during recording is negligible and also enables recording on plain paper without requiring fixing or other special treatment. Accordingly, interest in this method has been increasing.
A liquid jet recording method disclosed in Japanese Patent Application Laid-Open No. 54-51837 and German Application DOLS No. 2843064 has a feature different from a conventional liquid jet recording method in that heat energy is applied to liquid to generate a motive force to jet a liquid droplet.
The method disclosed in the above patent applications is characterized in that liquid acted on by the heat energy creates a change of phase which results in a rapid increase in volume and liquid is jetted from an orifice at an end of a recording head by an action due to the change of phase so that a flying liquid droplet is formed and deposited on a record medium to form a record.
Particularly, the liquid jet recording method disclosed in the German application DOLS No. 2843064 is not only effectively applicable to a so-called drop-on demand recording method but also enables implementation of a recording head of a full line type having a high density multi-orifice head. Thus, it can provide a high resolution and high quality image at a high speed.
The recording head used in a device for the above method includes a liquid jet unit having an orifice for jetting liquid and a liquid path communicating with the orifice for forming a heat applying unit which applies heat energy to the liquid to jet a liquid droplet, and an electro-thermal transducer for generating the heat energy.
The electro-thermal transducer includes a pair of electrodes and a heat generating resistance layer connected to the electrodes for defining a heat generating region (heat generating portion) between the electrodes. The electro-thermal transducer and the electrodes are usually formed in an upper layer of a base of the liquid jet recording head. FIGS. 1A and 1B show a prior known structure of the base having the electro-thermal transducer of the liquid jet recording head formed therein.
FIG. 1A shows a plan view around the electro-thermal transducer of the base of the liquid jet recording head and FIG. 1B shows a partial sectional view taken along a dot and dash line XY in FIG. 1A.
The base 101 of the liquid jet recording head comprises a bottom layer 106, a heat generating resistance layer 107, electrodes 103 and 104, a first upper protection layer 108, a second upper protection layer 109 and a third upper protection layer 110, laminated in this sequence on a base support 105.
The heat generating resistance layer 107 and the electrodes 103 and 104 are patterned in predetermined patterns by etching. They are patterned into the same pattern in areas other than an area of an electro-thermal transducer 102, and in the area of the electro-thermal transducer 102, the electrodes are not laminated on the heat generating resistance layer 107 and the heat generating resistance layer 107 forms a heat generating portion 111. The first upper protection layer 108 and the third upper protection layer 110 are laminated on the entire surface of the base 101 but the second upper protection layer 109 is not laminated on the electro-thermal transducer 102.
Materials of the upper layers of the base are selected in accordance with characteristics such as heat resistivity, liquid resistivity, thermal conductivity and insulation required by the areas on which the upper layers are located. A primary function of the first upper protection layer 108 is to maintain an insulation between the common electrode 103 and the selection electrode 104, a primary function of the second upper protection layer 109 is to prevent penetration of the liquid and to provide the liquid resistivity, and a primary function of the third upper protection layer 110 is to provide the liquid resistivity and reinforce a mechanical strength.
In the prior art liquid jet recording head having the base constructed as described above, when the base continuously contacts the liquid for a long time during repetitive use or a long-time continuous use, the upper protection layers formed on the base are peeled off so that the insulation is deteriorated, the electrodes or the electro-thermal transducers are broken and the supply of the liquid is impeded or the jetting of the liquid is blocked by deformation of the liquid path or the orifice.
One cause for the deterioration of the long-term liquid resistivity of the prior art liquid jet recording head may be considered as follows. Since a number of fine electro-thermal transducers are simultaneously formed on the base, the surface on which the upper protection layers are to be formed has fine concavo-convex steps. Accordingly, the upper protection layers do not perfectly cover the steps or defects such as pinholes are formed in the protection layers and the liquid penetrates through the defects.